1. Field of the Invention
The present invention relates to a method for manufacturing an optical sheet which controls an image light emitted from an image light source to output the light to the observer side, an optical sheet, and an image display device having the optical sheet.
2. Description of the Related Art
An image display device for outputting the image to the observer, such as liquid crystal display, plasma display, rear-projection display, organic EL, and FED, is provided with an image light source and an optical sheet comprising layers having various functions for improving the quality of an image light emitted from the image light source and outputting the image light to the observer.
There are several arts related to the optical sheets. For example, Patent document 1 (i.e. Japanese Patent Application Laid-open No. 2008-146074) discloses one of them. Patent document 1 focuses onto an external light shielding film (i.e. one of the layers constituting an optical sheet and is equivalent to the “optical functional sheet layer” of the present invention. Hereinafter, referred to as “optical functional sheet layer”.) and discloses a method for manufacturing the optical functional sheet layer. More specifically, Patent document 1 discloses a method characterized by filling more than once a light absorbing body made of a resin (i.e. equivalent to “binder made of resin” of the present invention. Hereinafter referred to as “binder”.) containing a light absorbing substance (i.e. equivalent to the “light-absorbing particle” of the present invention. Hereinafter, referred to as “light-absorbing particle”.) in a groove formed in the plane of the optical functional sheet layer. In the method for manufacturing the optical functional sheet layer described in Patent document 1, in view of filling the light absorbing body containing high density of the light-absorbing particles and improving function of external light shielding, preferably, the step of filling the light absorbing body is carried out more than once; and the density of the light-absorbing particles contained in the light absorbing body becomes higher each time.